The present invention relates to a process for crushing or pulverizing raw lignite or brown coal to fine coal.
For the pulverizing or normally moist raw brown coal to fine coal hitherto the brown coal has been passed through driers, in which e.g. an indirect steam heating of the coal has taken place and in this way the moisture has largely been removed from the coal. The raw lignite normally leaves such driers at a temperature of 70.degree. to 85.degree. C.
As these relatively high temperatures of 70.degree. to 85.degree. C. are extremely problematical with respect to an ignition or explosion of the coal dust mixture, the maximum permitted temperature for lignite dust has been set at 60.degree. C. in order to exclude the aforementioned hazards.
As a result of the starting temperature following the drying of the lignite of 70.degree. to 85.degree. C., the dried raw lignite is cooled to a temperature of approximately 40.degree. C. and this e.g. takes place in air-cooled drag chain conveyors.
The thus dried and cooled raw lignite has hitherto been comminuted and ground in continuous mills with crushing means, which are in particular in the form of rods or balls. In the case of these continuous mills e.g. designed as vibratory or agitator ball mills the comminution of the raw lignite mainly takes place between the crushing means and the crushing chamber wall. In said continuous mills as a result of the friction between the individual crushing means and between the crushing means and the crushing chamber wall heat is generated, which can lead to a marked temperature rise of e.g. 20.degree. C. in the dried raw lignite. The previously cooled raw lignite consequently again reaches the permitted temperature limit of approximately 60.degree. C.
In this hitherto used process it has proved to be particularly disadvantageous that the continuous mills used have a capacity limit of approximately 10 t/h with regard to the lignite throughout. Therefore in order to obtain a raw lignite throughput of approximately 60 t/h, as a function of the product fineness, it has hitherto been necessary to use six to ten such continuous mills, which in the preceding stages e.g. require four driers for the raw lignite with following the same four air-cooled drag chain conveyors.
Thus, the higher throughput capacity of a plurality of such units with a correspondingly larger number of drives, supply and discharge equipments, foundations, building with sound insulation and a higher monitoring and control expenditure.
However, it was necessary for the previously used process to limit the temperature of the raw lignite upstream of the mills to max. 40.degree. C., which could only be achieved by additional cooling units with a correspondingly high investment expenditure, space requirements and consequently transportation, control and maintenance costs.